It is common for bones to become fractured as the result of a fall, an automobile accident, a sporting injury, etc. In these circumstances, it is common to reinforce the bone in the area of the fracture so as to support the bone during healing.
To this end, current treatment options typically comprise external stabilizers (e.g., plaster casts, braces, etc.) and internal stabilizers (e.g., screws, bone plates, intramedullary nails, etc.).
External stabilizers such as casts and external braces suffer from a number of disadvantages. For one thing, they can interfere with a patient's normal daily activities, e.g., it can be difficult to wear clothing over a cast, or to operate a motor vehicle with a cast, etc. Furthermore, with animals, external casting and bracing of some fractures can be extremely difficult. In addition, with external stabilizers, the soft tissue interposed between the bone and the external stabilizer is used to transmit load from the bone to the external stabilizer. As a result, shortly after application of the external stabilizer, the patient's intervening soft tissue will begin to atrophy through disuse, thereby requiring further rehabilitation for the patient. Furthermore, as the intervening soft tissue atrophies, the close supporting fit of the external stabilizer is disrupted and, as a result, effective load transfer is undermined.
Internal stabilizers such as pins, screws, bone plates, intramedullary nails, etc. generally provide a more effective stabilization of the fracture, since they are able to directly interface with the bone. However, installing these internal stabilizers requires an invasive surgical procedure, e.g., a relatively large incision, etc. Furthermore, after healing of the fracture, the internal stabilizers (screws, bone plates, intramedullary nails, etc.) should, ideally, be removed so as to allow the bone to fully recover its mechanical strength. This, however, requires a second surgical procedure, with additional trauma to the patient.
In some circumstances (e.g., such as with fractures in vertebral bodies), bone cements may be injected into the interior of the bone in an attempt to stabilize the bone. However, such bone cements suffer from disadvantages of their own. More particularly, such bone cements are typically ceramic cements, polymer-based cements (e.g., polymethyl methacrylate, also known as PMMA) or calcium salt-based cements. While these bone cements are typically capable of withstanding significant compressive loading, they are also extremely brittle and typically cannot withstand significant tensile loading. This limits their application in instances where the loading on the bone may include a tensile component. This means that bone cements are not suitable for use in many situations, particularly in long bones (e.g., the tibia). Additionally, the failure mode for brittle materials results in catastrophic failure that includes the creation of shards of material which are difficult to remove and create potential dangers for the anatomy.
The aforementioned polymers and cements can be molded into useful shapes or injected (i.e., applied in situ) which results in an anisotropic alignment of the polymer crystals, or they can be drawn and annealed by extrusion or pultrusion methods, which align the polymer crystals in an isotropic manner such that a favored directional mechanical advantage can be established that is greater than the molded or injected method. This is the way some polymer pins are formed. There are drawbacks to this practice and the materials used. There remains a top strength to the final form that may not be appropriate for all bone-reinforcement activities. There is a limit to the diameter of the final form that can be aligned, since pultrusion and extrusion heat from the outside to aid in aligning the polymer crystals, and larger diameter devices will have a core of material which is not heated and therefore is not aligned. Finally, the isotropic alignment augments performance in one direction such as compression but may increase brittleness in side shear or torsion.
Thus it will be seen that a new approach is needed for treating bone fractures.
In addition to the foregoing, in some circumstances a medical condition (e.g., osteoporosis) can weaken or damage a bone, including the creation of voids within the bone, and it may be desirable to fortify and/or augment a bone so that it can better withstand the forces associated with normal physical activity. Unfortunately, however, the aforementioned external stabilizers, internal stabilizers and bone cements have all proven inadequate for fortifying and/or augmenting a bone, e.g., for the reasons given above.
Thus it will be seen that a new approach is also needed for fortifying and/or augmenting a bone.